In the drilling and completion industry, the formation of boreholes for the purpose of production or injection of fluid is common The boreholes are used for exploration or extraction of natural resources such as hydrocarbons, oil, gas, water, and alternatively for CO2 sequestration. For enhancing production and increasing extraction rates from a subterranean borehole, the formation walls of the borehole are fractured using a pressurized slurry, proppant containing fracturing fluid, or other treating fluids. The fractures in the formation wall are held open with the particulates once the injection of fracturing fluids has ceased.
A conventional fracturing system passes pressurized fracturing fluid through a tubular string that extends downhole through the borehole that traverses the zones to be fractured. The string may include valves that are opened to allow for the fracturing fluid to be directed towards a targeted zone. To remotely open the valve from the surface, a ball is dropped into the string and lands on a ball seat associated with a particular valve to block fluid flow through the string and consequently build up pressure uphole of the ball which forces a sleeve downhole thus opening a port in the wall of the string. When multiple zones are involved, the ball seats are of varying sizes with a downhole most seat being the smallest and an uphole most seat being the largest, such that balls of increasing diameter are sequentially dropped into the string to sequentially open the valves from the downhole end to an uphole end. Thus, the zones of the borehole are fractured in a “bottom-up” approach by starting with fracturing a downhole-most zone and working upwards towards an uphole-most zone.
While a typical frac job is completed sequentially in the bottom-up approach, an alternating stage process has been suggested in which a first interval is stimulated at a toe, a second interval is stimulated closer to the heel, and a third interval is fractured between the first and second intervals. Such a process has been indicated to take advantage of altered stress in the rock during the third interval to connect to stress-relief fractures from the first two intervals. However, accomplishing this process has only been capable with intervention requiring intricate manipulation from the surface or Intelligent Well System (“IWS”) technology.
The art would be receptive to alternative devices and methods for alternating a sequence of a frac job.